ON ANAESTHETICS 



279 



by a laborious chemical analysis, consists in the feeling of certainty 

 that irregularities of results, if present, are not due to instrumental irre- 

 gularities of quantity, but are in reality the expression of physiological 

 differences. As a matter of fact, however, under these conditions, 

 where there is no irregularity of chlorofoi'm percentage, there is a 

 remarkable regularity of physiological effects. 



A comparatively small number of experiments in which the chloro- 

 form percentage has been maintained scrupulously constant at, say, 

 2 per cent., while the oxygen percentage has been taken at and below 

 and above the normal — e.g., at 7 per cent., at 21 per cent., and at 

 97 per cent. 1 — enables us therefore to conclude with certainty that the 

 intensity of the chloroform effect is greater than normal at a lower 

 percentage of oxygen, less than normal at a higher percentage of 

 oxygen. The following experiments and records are given as being 

 representative : — 



Experiment 1, April 29. — To demonstrate the effect of excess and 

 deficiency of oxygen upon anaesthesia by chloroform vapour at 2 per 

 cent. 



Cat, 3'2 kilos., anaesthetised under a bell-jar by ether at an unknown 

 (high) percentage, subsequently maintained in anaesthesia of variable 

 depth by inhalations of chloroform at 2 per cent, as indicated in the 

 protocol. Each period of anaesthesia lasted for five minutes. The 

 depth of anaesthesia was gauged by the corneal reflex, which was more 

 or less brisk at the outset of each period, and more or less completely 

 abolished at the end of the period. When necessary the anaesthesia was 

 maintained by a sufficient amount of ether vapour. 



It is clear from this protocol that the effect of chloroform is regu- 

 larly greater and smaller with smaller and greater percentage of oxygen, 

 as gauged by the fall of blood pressure, the reduction of respiration, and 

 the abolition of the corneal reflex. From which it appears to be legi- 

 timate to infer that under such conditions oxygen has an influence 

 antagonistic to that of chloroform. This counteraction appears to hold 

 good for the higher and more dangerous percentages of chloroform, as 

 indicated by the next experiment. 



1 Brin's cylinders of oxygen, according to Mr. Gardner, have 97 per cent, of 

 oxygen and 3 per cent, of nitrogen. With 2 per cent, of chloroform the oxygen 

 percentage when Brin'i oxygen is employed is approximately 95 per cent. 



